26.remove-duplicates-from-sorted-array.cpp

/*
 * @lc app=leetcode id=26 lang=cpp
 *
 * [26] Remove Duplicates from Sorted Array
 *
 * https://leetcode.com/problems/remove-duplicates-from-sorted-array/description/
 *
 * algorithms
 * Easy (38.25%)
 * Likes:    1830
 * Dislikes: 3998
 * Total Accepted:    738.4K
 * Total Submissions: 1.7M
 * Testcase Example:  '[1,1,2]'
 *
 * Given a sorted array nums, remove the duplicates in-place such that each
 * element appear only once and return the new length.
 *
 * Do not allocate extra space for another array, you must do this by modifying
 * the input array in-place with O(1) extra memory.
 *
 * Example 1:
 *
 *
 * Given nums = [1,1,2],
 *
 * Your function should return length = 2, with the first two elements of nums
 * being 1 and 2 respectively.
 *
 * It doesn't matter what you leave beyond the returned length.
 *
 * Example 2:
 *
 *
 * Given nums = [0,0,1,1,1,2,2,3,3,4],
 *
 * Your function should return length = 5, with the first five elements of nums
 * being modified to 0, 1, 2, 3, and 4 respectively.
 *
 * It doesn't matter what values are set beyond the returned length.
 *
 *
 * Clarification:
 *
 * Confused why the returned value is an integer but your answer is an array?
 *
 * Note that the input array is passed in by reference, which means
 * modification to the input array will be known to the caller as well.
 *
 * Internally you can think of this:
 *
 *
 * // nums is passed in by reference. (i.e., without making a copy)
 * int len = removeDuplicates(nums);
 *
 * // any modification to nums in your function would be known by the caller.
 * // using the length returned by your function, it prints the first len
 * elements.
 * for (int i = 0; i < len; i++) {
 * print(nums[i]);
 * }
 */

// @lc code=start
class Solution {
 public:
  int removeDuplicates(vector<int>& nums) {
    if (nums.size() <= 1) {
      return nums.size();
    }

    int previous = nums[0];
    // slow index moves by 1 after every addition to the starting buffer
    int slow_index = 1;
    // fast index moves to the next non duplicate integer
    int fast_index = 1;

    while (fast_index < nums.size()) {
      if (nums[fast_index] == previous) {
        ++fast_index;
      } else {
        previous = nums[fast_index];
        nums[slow_index] = nums[fast_index];
        ++slow_index;
        if (slow_index > fast_index) {
          fast_index = slow_index;
        }
      }
    }

    return slow_index;
  }
};
// @lc code=end